How do you test to see if a double is equal to NaN

Question

I have a double in Java and I want to check if it is NaN  What is the best way to do this

User · Answer

Try Double isNaN        Returns true if this Double value is a Not-a-Number  NaN   false otherwise     Note that  double isNaN    will not work  because unboxed doubles do not have methods associated with them

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You might want to consider also checking if a value is finite via Double isFinite value   Since Java 8 there is a new method in Double class where you can check at once if a value is not NaN and infinity          Returns   code true  if the argument is a finite floating-point    value  returns   code false  otherwise  for NaN and infinity    arguments          param d the   code double  value to be tested     return   code true  if the argument is a finite    floating-point value    code false  otherwise      since 1 8     public static boolean isFinite double d

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Beginners needs practical examples  so try the following code   public class Not a Number    public static void main String   args           TODO Auto-generated method stub      String message    0 0 0 0 is NaN  nsimilarly Math sqrt -1  is NaN                String dottedLine    ------------------------------------------------             Double numerator   -2 0      Double denominator   -2 0            while  denominator  lt   1            Double x   numerator denominator                     Double y   new Double  x           boolean z   y isNaN            System out println  y        y           System out println  z        z           if  z    true               System out println message                                     else               System out println  Hi  everyone                       numerator   numerator   1          denominator   denominator  1          System out println dottedLine                     end of while       end of main       end of class

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If your value under test is a Double  not a primitive  and might be null  which is obviously not a number too   then you should use the following term   value  null    Double isNaN value   Since isNaN   wants a primitive  rather than boxing any primitive double to a Double   passing a null value  which can t be unboxed to a Double  will result in an exception instead of the expected false

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You can check for NaN by using var    var  NaN does not equal NaN   EDIT  This is probably by far the worst method  It s confusing  terrible for readability  and overall bad practice

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The below code snippet will help evaluate primitive type holding NaN   double dbl   Double NaN  Double valueOf dbl  isNaN     true   false

User · Answer

Use the static Double isNaN double  method  or your Double s  isNaN   method      1  static method if  Double isNaN doubleValue                  2  object s method if  doubleObject isNaN                  Simply doing   if  var    Double NaN                is not sufficient due to how the IEEE standard for NaN and floating point numbers is defined

[java] How do you test to see if a double is equal to NaN?

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